Mission-specific positron emission tomography

ABSTRACT

A handheld gamma camera or PET system with a disposable detector head is provided. This system includes a configuration of a gamma camera or PET scanner in which optical fibers or bundles of optical fibers are coupled to a scintillator or array of scintillators and the other end of the optical fibers or bundles of optical fibers are coupled to a light-sensitive camera, such as a photomultiplier. The system may further include a mechanism to rapidly couple and/or decouple the optical fiber or fibers from the light sensitive camera or from the scintillator or array of scintillators so that the detector can be disposed of or sterilized without damaging the light-sensitive camera. A method for image reconstruction and image simulation is also provided. The method includes an application of deterministic sampling using Gaussian quadrature parameters to construct a transition matrix for purposes of image reconstruction.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority under 35 U.S.C. 119(e) to U.S.Provisional Application Serial No. 60/402,535, entitled “MissionSpecific PET”, filed Aug. 12, 2002, the contents of which areincorporated by reference herein.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to an apparatus and a method fordetecting and delineating cancerous lesions, and more particularly anapparatus and a method for effective and affordable early detection ofcancerous lesions using gamma rays or other radiation to obtain imagedata.

[0004] 2. Description of the Related Art

[0005] As medical therapies become more biochemically specific, medicalresearchers and practitioners have turned to molecular imaging todevelop new therapies and guide treatment with these therapies. Positronemission tomography (“PET”) is the archetypal molecular imaging device,due to its high sensitivity to extremely small amounts ofbiochemically-relevant molecular probes. With such small amounts (e.g.,tracer quantities), it is possible to monitor biochemical processeswithout substantially altering enzymatic kinetic rates.

[0006] The detection of early primary cancers with whole-body PET hasbeen less successful than the detection of metastatic activity. Thisperformance difference has been ascribed to instrumental limitations, aswell as biological differences between primary cancers as compared tometastases. In general, it is preferable to detect primary cancers whenthey are small, since the chances of cure and control are substantiallyincreased. The small size of early cancer reduces lesion detectabilitybecause of the finite resolution of the PET device, which effectivelyreduces lesion-to-background contrast. In the PET field, reducedlesion-to-background contrast can be quantitatively measured with therecovery coefficient. This effect has been extensively explored inphantom and clinical trials by Dr. Lee Adler. For example, see“Simultaneous Recovery of Size and Radioactivity Concentration of SmallSpheroids with PET Data”, C. Chen, L. Adler et al., J. Nucl. Med. 40(1),1999, pp. 118-130; and “A Non-Linear Spatially Variant Object-DependentSystem Model for Prediction and Correction of Partial Volume Effect inPET”, C. Chen, L. Adler et al., IEEE Trans. Med. Imag. 17:214-227, 1998.

[0007] In U.S. patent application Ser. No. 09/737,119, Publication No.20010040219, Cherry et al. disclose a detector for use in a dedicatedPET scanner for cancer applications, particularly breast cancerapplications, using at least two detector plates containing arrays ofLSO or light-equivalent scintillating crystals and a fiber-optic bundleserving as a light-guide between the scintillator arrays andphotomultiplier tubes. However, in the Cherry system, a fiber-opticbundle must be placed in at least two detector plates. In addition, inthe Cherry system, the fiber-optic light guides are attached to thescintillator arrays and to the photomultipliers permanently, and theseattachments are fixed and not removable. Such a fixed and non-removablearrangement may lead to practical difficulties when, for example, amedical intervention using data provided by the system requires physicalaccess that may be obstructed by the fibers, or when the scintillatorarrays and/or fiber optics are contaminated by body fluids so as torequire disposal or sterilization. Thus, there is a need for a moreflexible PET scanner system that allows the optical fibers to beremovable from a photomultiplier or scintillator.

SUMMARY OF THE INVENTION

[0008] Advantageously, the invention provides a new algorithm forimaging reconstruction and simulation methods, including an applicationof Monte Carlo methods or deterministic sampling using Gaussianquadrature to constructing a transition matrix for purposes of iterativeimage reconstruction. The invention also provides the advantageousfeature of an application of deterministic sampling using Gaussianquadrature to perform a transport calculation for purposes of simulatinga medical imaging system which is sensitive to gamma-ray or otherradiation emitted by the body.

[0009] In another aspect, the invention advantageously provides ahandheld gamma camera or PET system with a disposable detector head,including a configuration of a gamma camera or PET scanner in whichoptical fibers or bundles of optical fibers are coupled to ascintillator or array of scintillators and the other end of the opticalfibers or bundles of optical fibers are coupled to a light-sensitivecamera (for example a photomultiplier). The invention may furtherinclude a mechanism to rapidly couple and/or decouple the optical fiberor fibers from the light sensitive camera or from the scintillator orarray of scintillators so that the detector can be disposed of orsterilized without damaging the light-sensitive camera. The inventionmay further include a configuration in which a fiber-optic array couplesone detector plate to a light-sensitive camera, while a second detectorplate does not require a fiber-optic array.

[0010] In another aspect, the invention advantageously provides afree-hand scanner using the aforementioned new algorithm for imagingreconstruction and simulation to generate a transition matrix (whichrelates response of detector geometric properties to source geometry)which is used to reconstruct images.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 shows a diagram of a PEM-2400 dedicated breast cameramounted in a stereotactic x-ray mammography unit.

[0012]FIG. 2 shows a hot spot phantom diagram that illustrates clearvisualization of 1.5 mm hot spots.

[0013]FIG. 3 shows a graph of an exemplary position of detector headsfrom a hand-held PET scanner.

[0014]FIG. 4 illustrates an exemplary diagram of a graphical userinterface that shows hand-held PET scanner detector heads as rigidbodies, with lines of response generated by a source between thedetector heads.

[0015]FIG. 5 shows an exemplary graph of an energy spectrum of a crystalin a compact array for endoscopy.

[0016]FIG. 6 shows a side view of a detector array according to apreferred embodiment of the invention. The detector array comprisesscintillating crystals, each of which is attached to a fiber-optic tail.The fiber-optic tails which are arranged in a bundle.

[0017]FIG. 7 shows a diagram of the fiber optics as they separate fromthe bundle and are attached to a position-sensitive photomultiplierface, as constructed according to a preferred embodiment of theinvention.

[0018]FIG. 8 shows a schematic drawing of a prostate imaging devicehaving biopsy and ultrasound compatibility, according to a preferredembodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0019] Reduced lesion detectability due to resolution limitations is awell-known phenomenon in the medical imaging arena. For example, theexacting requirements of breast cancer detection have led toconstruction of ultrahigh resolution x-ray devices, specificallydesigned for breast imaging. Naviscan PET Systems (formerly known as PEMTechnologies) has set the standard for dedicated breast imaging usingPET; for example, see U.S. Pat. No. 5,252,830. The first Naviscan PETSystems product was a breast-specific PET scanner with better than 3-mmfull-width half maximum [FWHM] spatial resolution.

[0020] Just as in x-ray imaging, there are often good reasons to buildmission-specific PET imaging devices. Building a whole-body PET scannerwith 2-mm resolution, as would be required to reliably detect earlycancers in the breast, would be very expensive. Whole-body PET scannersutilize hundreds of expensive photomultipliers which result inresolutions on the order of 6-mm FWHM. Improving spatial resolution by afactor of three, as would be needed to significantly reduce contrastrecovery problems, would require replacing conventional photomultipliersby even more expensive models, substantially increasing constructioncosts. Although ingenious schemes have been developed that attempt toreduce construction costs of high resolution PET systems, these methodshave yet to be applied to commercially available whole-body products,and would in any case be just as effective in reducing the cost ofsmaller dedicated mission-specific instruments. In a dedicated breastPET device, since the field of view is restricted to the breast,reaching even sub-millimeter resolution, as has been achieved by usingof state-of-the-art technology, could potentially become affordable.

[0021] Aside from purely economic considerations, there are functionsthat are considered necessary for certain clinical missions that aredifficult if not impossible to deliver with conventional whole-body PETscanners. These functions relate to cross-modality correlations (e.g.,with ultrasound or x-ray mammography) and interventional/biopsycapability. Newly-introduced imaging devices that combine PET with x-raycomputed tomography (i.e., PET/CT scanners) can be used to performbiopsy of lesions in stable organs (e.g., liver metastases), but wouldbe difficult to use for mobile organs that are less amenable toCT-guided biopsy (e.g., ovary or bowel). With respect tointerventional/biopsy capability, short scan times are highly desirable,and dedicated PET instruments can benefit from significantly increasedcollection efficiencies as compared to conventional ring scanners. Inthe case of dedicated breast PET, the combination of reduced attenuationlosses (e.g., 5 cm of fatty breast tissue as compared to 50 cm of chestand breast) and increased solid angle coverage—due to reduced r-squareddistance between the body part and the detector—can dramaticallydecrease scan time required to confidently visualize subtle lesions. Itis noted that a lesion is defined as a local area in the body which maybe harmful to the patient. For example, a lesion may be a cancer, aninflammatory process, or a necrotic area of tissue.

[0022] Not all clinical problems merit the development ofmission-specific scanners. However, Naviscan PET Systems has identifiedseveral medical market niches in oncology that may justify thedevelopment and commercialization of such products: breast, prostate,ovary, and liver metastases. Outside of oncology, there are potentialapplications to cardiac surgery and treatment of infectious disease; forexample, selection of appropriate borders for amputation inosteomyelitis, and selection of locations for endoscopic biopsy intuberculosis. From a commercialization point of view, there are severalexamples of mission-specific products that have been highly valued inthe marketplace once reimbursement patterns became well-defined.Examples include bone densitometry and spot digital mammography forbreast biopsy.

[0023] From a public health point of view, the construction ofcost-effective devices incorporating PET technology enables diffusion ofmolecular imaging into the broader medical community. This pattern isexpected to improve delivery of health care to the public by allowingnon-radiological specialists to deliver therapy on a more rational basis(e.g., on the basis of individual biochemistry profiles), consistentwith current concepts in oncology which look at the individual's tumortype as only the first step in choosing tailored therapy.

[0024] Outside of oncology, PET has been shown to be effective inpredicting myocardial viability. If a portable PET scanner is availablefor use in the cardiac surgery suite, it may be possible to immediatelyassess the adequacy of supply to reperfused myocardium. Portable PETscans can be used to guide bone removal in osteomyelitis, potentiallyreducing the degree of amputation required to effect a cure.

[0025] Monte Carlo methods may be used advantageously in conjunctionwith the present invention. Historically, simulation studies were firstdeveloped when experiments were prohibitive in cost, time, or otherfactors. Von Neumann coined the phrase Monte Carlo when he appliedrandom sampling to calculate neutron diffusion rates during theManhattan Project. Monte Carlo simulations are based on the constructionof a stochastic model in which the expectation value of a randomvariable is equivalent to the measured physical quantity. Thisexpectation value is estimated by the average of multiple independentsamples representing this random variable, obtained by random sampling.For example, consider a random variable X which is needed for a probleminvolving photon propagation in tissue. This variable might be the angleof deflection a scattered photon may experience due to a scatteringevent. Associated with this random variable is a probability densityfunction over a given interval. The integral of this probability densityfunction is normalized to unity over this interval, which corresponds tothe fact that any sampling of the random variable must lie in the giveninterval. To model a more complex system, the outcomes of each randomsampling are accumulated under appropriate weights and any rejectionalgorithms to arrive at an expected value of a given measurable physicalquantity.

[0026] Monte Carlo techniques were introduced into medical physics byRaeside in 1976 and to PET by Keller in 1983. Full PET devices have beensimulated using GEANT, a code developed by high energy physicists thatincluded the ability to specify detector geometry, and with adaptationsof older codes developed by Keller and Lupton. These simulations havemodeled classic ring geometries for PET devices for both human andanimal varieties. Works-in-progress presentations have been made aboutparallel-plate and square detector rings.

[0027] Preliminary results have been obtained by the present inventorsdemonstrating proof-of-principle for an endoscopic PET scanner and for anovel application of code to replace traditional Monte Carlocalculations. Naviscan PET Systems has used Monte Carlo methodsextensively in conducting simulations of both fixed and free-handgeometries. For example, Monte Carlo methods have been used to createtransition matrices for reconstruction. Specifically, these methodsrelate to the reconstruction that is required to provide a high qualityimage of an unknown distribution of radioactive sources. Reconstructionis often performed with an iterative technique, in which a computercompares the calculated response of the imaging system to successiveguesses as to the distribution with the actual measured response asmeasured by the imaging system. In order to calculate the response ofthe imaging system to these guesses, a “transition matrix” is used tomodel the imaging system. In most imaging devices, this transitionmatrix is generated by examining a fixed detector geometry and a fixedvolume in which the unknown radioactive source distribution is allowedto occupy. In accordance with an embodiment of the invention, for moreflexible imaging systems, the position of a freed detector head isdetermined, and the transition matrix is calculated using Monte Carlo ordeterministic sampling methods. In accordance with another embodiment ofthe invention, Monte Carlo and/or deterministic sampling methods may beused for modeling systems with the aim of improving design.

[0028] It is known that a transition matrix that models the response ofthe detection system to arbitrary distributions of radioactivity isneeded in order to assist a PET system in performing image formation(e.g., through iterative image reconstruction). Other types ofreconstructions, such as filtered backprojections, may also employtransition matrices to form an image. According to a preferredembodiment of the present invention, the use of Monte Carlo and/ordeterministic sampling methods allow the PET system to have greatflexibility, because the trajectory of the fiber-optic mountedscintillator can be tracked by a position sensor. This trajectory can beinputted into the Monte Carlo and/or deterministic sampling algorithm tocreate a transition matrix for a PET or gamma ray imaging systemincorporating the tracked fiber-optic mounted scintillator array. Theimaging system may include other components, possibly using timingcoincidence (also referred to as coincidence gating, or coincidentgating). Specifically, the other components may include a detector platemounted outside the body. Additionally, tracking of the fiber-opticmounted scintillator array may be accomplished with a method other thana position sensor, for example, by using a position encoder such as amoveable lever that can place the scintillator array in a known set ofpositions.

[0029] Coincidence gating is the method of aggregating events dependingon the period of time between detection of these events by the imagingsystem. Coincidence gating can be applied in electronic form (e.g., withAND circuitry that only allows pulses within a specific time interval togenerate a gate signal), or post-acquisition by examination of listfiles showing when each event was detected by the imaging system. Otherforms of coincidence gating or detection may be used as well.

[0030] As is traditional for light guide fabricators, dedicated breastimaging PET designs were performed with the assistance of Monte Carlomodels, which enabled clear identification of 2-mm crystal pitches withvery low profile light guides. These low-profile light guides enabledthe building of PET detector heads for mammography that were verycompact (e.g., less than 6 cm deep). Referring to FIG. 1, a diagram of aPEM-2400 breast camera mounted in a Lorad stereotactic x-ray mammographyunit is shown. These detector heads are so small that they can staymounted in a stereotactic mammography camera without requiring removalof the x-ray detector. Referring to FIG. 2, an exemplary hot spotphantom diagram that illustrates clear visualization of 1.5 mm hot spotscan be obtained from a camera such as that illustrated in FIG. 1.

[0031] Referring to FIGS. 3 and 4, for free-hand geometries, it ispossible to collect the information about the orbits experienced by ahand-held scanner and project all possible line-pairs from a sourcevolume that could be intercepted by the scanner traversing the orbit. InFIG. 3, an exemplary position of detector heads from a hand-held PETscanner is shown. FIG. 4 illustrates an exemplary diagram of a graphicaluser interface that shows hand-held PET scanner detector heads as rigidbodies, with lines of response generated by a source between thedetector heads, including lines of response for zero attitude 405,azimuth rotation 410, elevation rotation 415, and roll rotation 420. Thepresent inventors have extended this principle to allow the orbit itselfto be specified through a random walk, in order to compare variousdetector geometries. Prototype free-hand SPECT and PET devices have beenbuilt, which are able to image point sources and remove overlappingactivity by using Monte Carlo based reconstructions.

[0032] For a stochastic orbit, the field-of-view of the system isconstrained mathematically within a specified detection volume in whichthe detectors can be located.

[0033] Naviscan PET Systems has pioneered adoption of a newcomputational method that promises to significantly reduce computationaltime for simulations. This method incorporates deterministic samplingusing Gaussian quadrature, and has been shown to speed up transportcodes in plasma physics by a factor of one thousand. The code is fast,efficient, rapidly convergent, and highly parallelizable. It is based ona technique of replacing each call to a random number generator with acarefully chosen and deterministic realization of the random variable.In other words, in place of calling a random number generator, theweights and abscissas of the relevant Gaussian quadrature parameters areused. For example, in many imaging algorithms, a Monte Carlo calculationrequires a random realization of the random variable N(0,1) (i.e., arandom variable of mean zero and variance unity) defined by a Gaussianprobability density function p(x)=exp(−x²/2). In the case of p(x), therelevant Gaussian quadrature parameters are simply the well-knownGauss-Hermite weights w_(j) and abscissas q_(j). For example, instead ofmaking two Monte Carlo random samplings, two deterministic samplings areobtained from the n=2 Gauss-Hermite abscissa-weight pairs. For n=2,these pairs are simply q_(j)=(−0.57735, +0.57735) and w_(j)=(1, 1).

[0034] This method is based on exploiting a theorem from Gaussianintegration that states that for a function f(x), the followingapproximation:${\int_{- \infty}^{\infty}{{f(x)}\quad {\exp \left( {{- x^{2}}/2} \right)}\quad {x}}} \approx {\sqrt{2\pi}{\sum\limits_{j = 1}^{J}\quad {w_{j}{f\left( q_{j} \right)}}}}$

[0035] becomes exact if the weights w_(j) and abscissas q_(j) areGauss-Hermite and the function j(x) is a linear combination of the 2J−1polynomials x⁰, x¹, . . . , x^(2J−1).

[0036] In addition to compact light guides for breast imaging, thepresent inventors have developed compact cameras for endoscopy that fiton fiber optic bundles according to a preferred embodiment of theinvention. Referring to FIG. 5, an exemplary energy spectrum for one of24 crystals in an array is shown. In example shown in FIG. 5, thecrystal that produced the energy spectrum is approximately 2 mm thick,and the compact array has a diameter of approximately 1 cm. Referring toFIG. 6, an exemplary array design for a detector head of the endoscopycamera is shown. In this example, the detector head includes a total of32 lutetium oxyorthosilicate (“LSO”) crystals 605, arranged in an 8×4array. Each LSO crystal 605 is 2 mm×4 mm×5 mm. Thus, in this example,the total volume required by the detector head is approximately 1.3 cm³.A conventional small field-of-view array volume is about 43 cm³, whichis about 33 times as large as that depicted in FIG. 6. Thus, thedetector shown in FIG. 6 represents an improved pixel resolution of afactor of 33. For example, if a conventional detector yields a countrate of 1 kHz, then the detector of FIG. 6 will yield a count rate ofabout 30 Hz, which is equivalent to about 1 true Hz per pixel. Inaddition, each LSO crystal 605 couples with seven optical fibers, andthe coupling between the crystal 605 and the fibers is designed so thatthe fibers can be easily decoupled from the crystal. In other words,although the fibers are actually physically attached to the crystal, thefibers are removable and disposable, for situations in which, forexample, a medical intervention requires access that would otherwise beobstructed by the fibers. The quality of removability of the fibers maybe implemented by fiber-optic couplers and ferrules, or by otherconventional methods of coupling fiber-optic bundles to imaging devicesor to other fiber-optic bundles. Referring to FIG. 7, a cross-sectionalview of a six-by-six array is also shown, including several fiber opticbundles 705 on the face 710 of the camera. Each of the fiber opticbundles 705 includes seven fibers, each of which is approximately 1 mmin diameter.

[0037] Referring to FIG. 8, the present invention further provides adesign for a prototype endoscopic PET camera. This camera has twocomponents, including an ultra-compact endoscopic component 805 incoincidence with a larger external component 810, similar to a devicefor prostate imaging as disclosed in U.S. patent application Ser. No.10/196,560. The device includes two components: (1) an ultra-compactintracavitary component 805 comprising a small (e.g., 1 cm diameter)array of thin (e.g., 2 mm by 5 mm) LSO crystals mounted on fiber opticsthat are attached to a position-sensitive photomultiplier, and (2) anexternal component array 810 of detectors and photomultipliers placedanterior or posterior to the patient. In principle, placing detectors onthe ends of fibers has been done before (e.g., for animal scanners),although the motivation in those cases was to allow deployment of largephotomultipliers in observing a small volume. Gamma detectors have alsobeen placed on the ends of fiber optics in order to build non-imaginggamma probes. The present inventors have extended these concepts tobetter suit the needs of endoscopists, by making several enablingmodifications, including the following: 1) introducing a quick-releaseoptical fiber coupling so that the detector head is separable from thephotomultiplier, and is therefore disposable; 2) adding position sensingto the detector head so that events can be correctly placed insinograms; 3) including flexible Monte Carlo-based reconstructionalgorithms to allow reconstruction of events from the mobile detectorhead and a second detector head placed external to the body; and 4)using deterministic sampling to accelerate these reconstructionalgorithms. These advantageous features allow the present invention tobe useful to surgeons and endoscopists, who can kill or remove cancer orinflammatory cells and then use the present invention to check to ensurethat the cells are actually removed or dying. Then, the presentinvention can be further utilized to check the field of surgery (orother therapy) to determine whether residual viable cells are present,proceeding iteratively to minimize the number of residual viable cells.

[0038] While the present invention has been described with respect towhat is presently considered to be the preferred embodiment, it is to beunderstood that the invention is not limited to the disclosedembodiments. To the contrary, the invention is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims. For example, the above descriptions ofembodiments of the invention are primarily couched in terms of using aPET scanner system. Those skilled in the art will understand that acompact gamma camera system using coincidence gating (i.e., a coincidentgamma camera system) may also be used. The scope of the following claimsis to be accorded the broadest interpretation so as to encompass allsuch modifications and equivalent structures and functions.

[0039] The contents of each of the following publications are herebyincorporated by reference:

[0040] 1) S. Holbrook, “Newsline Commentary”, Journal of NuclearMedicine 43(2), p. 12N, 2002.

[0041] 2) L. P. Adler et al., “Evaluation of Breast Masses and AxillaryLymph Nodes with [F-18] 2-Deoxy-2-fluoro-D-glucose PET”, Radiology,1993, 187: 743-750.

[0042] 3) B. Fisher et al., “Cancer of the Breast: Size of Neoplasm andDiagnosis”, Cancer, 1969, 24:1071-1080.

[0043] 4) R. M. Kessler et al., “Analysis of emission tomographic scandata: limitations imposed by resolution and background”, J. Comput.Assist Tomography, 1984, 8:514-522.

[0044] 5) C. Chen, L. Adler et al., “Simultaneous Recovery of Size andRadioactivity Concentration of Small Spheroids with PET Data”, J. Nucl.Med., 40(1), pp. 118-130, 1999.

[0045] 6) C. Chen. L. Adler et al., “A non-linear spatially-variantobject-dependent system model for prediction and correction of partialvolume effect in PET”, IEEE Trans. Med. Imag., 17: 214-227, 1998.

[0046] 7) U.S. Pat. No. 5,252,830.

[0047] 8) I. Weinberg et al., “Preliminary Results for Positron EmissionMammography: Real-Time Functional Breast Imaging in a ConventionalMammography Gantry”, Eur. J. Nucl. Med., 23(7):804-806, 1996.

[0048] 9) R. Miyaoka, “Dynamic high resolution positron emission imagingof rats”, Biomed. Sci. Instrum. 1991, 27:35-42.

[0049] 10) D. Townsend et al., “High Density Avalanche Chamber (HIDAC)Positron Camera”, J. Nucl. Med., 28:1554-1562, 1987.

[0050] 11) C. Thompson et al., “Feasibility Study for Positron EmissionMammography”, Med. Phys. 1994, 21:529-538.

[0051] 12) R. Ott, “The Applications of Positron Emission Tomography toOncology”, Br. J. Cancer, 1991, 63:343-345.

[0052] 13) J. Tillisch et al., “Reversibility of cardiac wall motionabnormalities predicted by positron emission tomography”, New Engl. J.Med. 314: 884-8, 1986.

[0053] 14) D. McCracken, “The Monte Carlo method”, Sci. Am. 192, 90-96(1955).

[0054] 15) D. Raeside, “Monte Carlo principles and applications”, Phys.Med. Biol. 21, 181-197 (1976).

[0055] 16) N. Keller and J. Lupton, “PET detector ring aperture functioncalculations using Monte Carlo techniques”, IEEE Trans. Nucl. Sci. 30,pp. 676-680 (1983).

[0056] 17) C. Thompson et al., “PETSIM: Monte Carlo simulation of allsensitivity and resolution parameters of cylindrical positron imagingsystems”, Phys. Med. Biol., 1992, Vol. 37(3), pp. 731-749.

[0057] 18) W. Moses et al., “Design of a High Resolution, HighSensitivity PET Camera for Human Brains and Small Animals”, IEEETransactions on Nuclear Science NS-44, pp. 1487-1491, 1977.

[0058] 19) W. Worstell et al., “Monte Carlo-based Implementation of theML-EM Algorithm for 3-D PT Reconstruction”, Proceedings IEEE Nucl. Sci.Symp. 1997.

[0059] 20) 1. Weinberg et al., “Crystal Identification in Modular2-Dimensional Array Detectors for High Spatial Resolution PET”, Proc.Intl. Wksp. on Physics and Engineering in Computerized Multi-dimensionalImaging and Processing, SPIE V.

[0060] 21) 1. Weinberg et al., “Biopsy-Ready PEM Scanner with Real-TimeX-Ray Correlation Capability”, accepted for presentation at IEEE Nucl.Sci. Symp. 2002.

[0061] 22) I. Weinberg et al., “Implementing reconstruction withhand-held gamma cameras”, Proceedings IEEE Nuc. Sci. Symp. 2000.

[0062] 23) D. S. Lemons and B. J. Albright, “Quiet Monte-Carlo radiationtransport”, Journal of Quantitative Spectroscopy and Radiation Transfer,Vol. 74, pp. 719-729 (2002).

[0063] 24) U.S. patent application Ser. No. 10/196,560, filed Jul. 17,2002.

[0064] 25) A. Chatziioannou et al., “Performance Evaluation ofMicro-PET: A High-Resolution Lutetium Orthosolicate PET Scanner forAnimal Imaging”, J. Nucl. Med. 1999, 40:1164-1175.

[0065] 26) F. Daghighian, et al., “Intraoperative beta probe: a devicefor detecting tissue labeled with positron or electron emitting isotopesduring surgery”, Med. Phys., Vol. 21(1), pp.153-157, January 1994.

[0066] 27) U.S. application Ser. No. 09/737,119, Publication No.20010040219, filed Dec. 14, 2000.

[0067] 28) U.S. application Ser. No. 09/833,110, filed Apr. 11, 2001.

[0068] 29) U.S. Pat. No. 6,331,703.

[0069] 30) U.S. patent application Ser. No. 10/027,759, filed Dec. 21,2001.

What is claimed is:
 1. A positron emission tomography (PET) scannersystem for obtaining image data relating to a body part, the systemincluding a first detector head and a second detector head, the firstdetector head comprising: a light-sensitive camera or array oflight-sensitive cameras; at least one scintillator; a plurality ofoptical fibers coupled to the at least one scintillator; and a mechanismconfigured to rapidly couple and/or decouple the optical fibers to orfrom the light-sensitive camera or the array of cameras or the at leastone scintillator, and the second detector head comprising materials thatare sensitive to radiation being emitted by the body part, whereincoincidence gating is applied between signals detected by the first andsecond detector heads.
 2. The scanner system of claim 1, wherein thefirst detector head is configured to be positioned within a body cavity,and the second detector head is configured to be positioned external tothe body part.
 3. The scanner system of claim 2, wherein the system isconfigured to apply Monte Carlo methods to construct a transition matrixfor a purpose of image reconstruction.
 4. The scanner system of claim 3,further comprising at least one position sensor, the at least oneposition sensor being configured to determine a location of the firstdetector head and/or a location of the second detector head.
 5. Thescanner system of claim 3, further comprising at least one positionencoder, the at least one position encoder being configured to determinea location of the first detector head and/or a location of the seconddetector head.
 6. The scanner system of claim 1, wherein the at leastone scintillator comprises a compact array of scintillating crystals,each crystal having a length, a width, and a depth, and wherein each ofthe length, the width, and the depth of each crystal is less thanapproximately 10 millimeters.
 7. The scanner system of claim 6, whereinthe compact array of scintillating crystals has a volume, the volumebeing equal to a product of a number of crystals in the array and thelength, the width, and the depth of each crystal, and wherein the volumeis less than approximately 2.0 cubic centimeters.
 8. The scanner systemof claim 1, wherein the scanner system is configured to applydeterministic sampling using Gaussian quadrature parameters to constructa transition matrix for a purpose of image reconstruction.
 9. Thescanner system of claim 1, wherein the scanner system is configured toapply deterministic sampling using Gaussian quadrature parameters toperform a transport calculation for a purpose of simulating a medicalimaging system which is sensitive to radiation emitted by the body part.10. The scanner system of claim 8 or claim 9, wherein the Gaussianquadrature parameters are the Gauss-Hermite weights w_(j) and abscissasq_(j).
 11. The scanner system of claim 1 or claim 2, wherein the bodypart comprises one of the group consisting of the breast, the prostate,the ovary, and the liver.
 12. The scanner system of claim 1 or claim 2,wherein the body part comprises a bone.
 13. A coincident gamma camerasystem for obtaining image data relating to a body part, the systemincluding a first detector head and a second detector head, the firstdetector head comprising: a gamma camera or array of gamma cameras; atleast one scintillator; a plurality of optical fibers coupled to the atleast one scintillator; and a mechanism configured to rapidly coupleand/or decouple the optical fibers to or from the gamma camera or thearray of gamma cameras or the at least one scintillator, and the seconddetector head comprising materials that are sensitive to gamma radiationbeing emitted by the body part, wherein coincidence gating is appliedbetween signals detected by the first and second detector heads.
 14. Thecoincident gamma camera system of claim 13, wherein the first detectorhead is configured to be positioned within a body cavity, and the seconddetector head is configured to be positioned external to the body part.15. The coincident gamma camera system of claim 14, wherein the systemis configured to apply Monte Carlo methods to assist in an imagereconstruction or in an image formation.
 16. The coincident gamma camerasystem of claim 15, further comprising at least one position sensor, theat least one position sensor being configured to determine a location ofthe first detector head and/or a location of the second detector head.17. The coincident gamma camera system of claim 15, further comprisingat least one position encoder, the at least one position encoder beingconfigured to determine a location of the first detector head and/or alocation of the second detector head.
 18. The coincident gamma camerasystem of claim 13, wherein the at least one scintillator comprises acompact array of scintillating crystals, each crystal having a length, awidth, and a depth, and wherein each of the length, the width, and thedepth of each crystal is less than approximately 10 millimeters.
 19. Thecoincident gamma camera system of claim 18, wherein the compact array ofscintillating crystals has a volume, the volume being equal to a productof a number of crystals in the array and the length, the width, and thedepth of each crystal, and wherein the volume is less than approximately2.0 cubic centimeters.
 20. The coincident gamma camera system of claim13, wherein the system is configured to apply deterministic samplingusing Gaussian quadrature parameters to assist in an imagereconstruction or in an image formation.
 21. The coincident gamma camerasystem of claim 13, wherein the system is configured to applydeterministic sampling using Gaussian quadrature parameters to perform atransport calculation for a purpose of simulating a medical imagingsystem which is sensitive to radiation emitted by the body part.
 22. Thecoincident gamma camera system of claim 20 or claim 21, wherein theGaussian quadrature parameters are the Gauss-Hermite weights w_(j) andabscissas q_(j).
 23. The coincident gamma camera system of claim 13 orclaim 14, wherein the body part comprises one of the group consisting ofthe breast, the prostate, the ovary, and the liver.
 24. The coincidentgamma camera system of claim 13 or claim 14, wherein the body partcomprises a bone.
 25. An apparatus for obtaining image data relating toa body part, the apparatus comprising a first detecting means and asecond detecting means, the first detecting means: a light-sensitivecamera means or array of light-sensitive camera means for recordingimage data; at least one scintillator means; a plurality of opticalfiber means coupled to the at least one scintillator; and a decouplingmeans for rapidly coupling and/or decoupling the optical fibers to orfrom the light-sensitive camera means or the array of camera means orthe at least one scintillator means, and the second detecting meanscomprising materials that are sensitive to radiation being emitted bythe body part.
 26. The apparatus of claim 25, wherein the firstdetecting means is configured to be positioned within a body cavity, andthe second detecting means is configured to be positioned external tothe body part, and wherein coincident gating is applied between signalsdetected by the first and second detecting means.
 27. The apparatus ofclaim 26, wherein the apparatus is configured to apply Monte Carlomethods to construct a transition matrix for a purpose of imagereconstruction.
 28. The apparatus of claim 27, further comprising atleast one position sensing means for determining a location of the firstdetecting means and/or a location of the second detecting means.
 29. Theapparatus of claim 27, further comprising at least one position encodingmeans for determining a location of the first detecting means and/or alocation of the second detecting means.
 30. The apparatus of claim 25,wherein the at least one scintillator means comprises a compact array ofscintillating crystals, each crystal having a length, a width, and adepth, and wherein each of the length, the width, and the depth of eachcrystal is less than approximately 10 millimeters.
 31. The apparatus ofclaim 30, wherein the compact array of scintillating crystals has avolume, the volume being equal to a product of a number of crystals inthe array and the length, the width, and the depth of each crystal, andwherein the volume is less than approximately 2.0 cubic centimeters. 32.The apparatus of claim 25, wherein the apparatus is configured to applydeterministic sampling using Gaussian quadrature parameters to constructa transition matrix for a purpose of image reconstruction.
 33. Theapparatus of claim 25, wherein the apparatus is configured to applydeterministic sampling using Gaussian quadrature parameters to perform atransport calculation for a purpose of simulating a medical imagingsystem which is sensitive to radiation emitted by the body part.
 34. Theapparatus of claim 32 or claim 33, wherein the Gaussian quadratureparameters are the Gauss-Hermite weights w_(j) and abscissas q_(j). 35.The apparatus of claim 25 or claim 26, wherein the body part comprisesone of the group consisting of the breast, the prostate, the ovary, andthe liver.
 36. The apparatus of claim 25 or claim 26, wherein the bodypart comprises a bone.
 37. A method of reconstructing image data todetect or delineate a lesion in a body part using a positron emissiontomography (PET) scanning system having at least a first detector headand a second detector head, the first and second detector heads beingsensitive to radiation emitted by the body part, and the methodcomprising the steps of: positioning the first detector head within abody cavity; positioning the second detector head external to the bodypart; using coincidence gating to record data obtained by the first andsecond detector heads from the radiation emitted by the body part; andapplying deterministic sampling using Gaussian quadrature parameters toassist in an image reconstruction or in an image formation using therecorded data.
 38. The method of claim 37, wherein the first detectorhead is coupled to a plurality of optical light fibers, and wherein theplurality of optical light fibers are configured to be detachable fromthe first detector head.
 39. The method of claim 37, wherein theGaussian quadrature parameters used for constructing the transitionmatrix are the Gauss-Hermite weights w_(j) and abscissas q_(j).
 40. Amethod of reconstructing image data to select borders for amputation ofa body part using a positron emission tomography (PET) scanning systemhaving at least a first detector head and a second detector head, thefirst and second detector heads being sensitive to radiation emitted bythe body part, and the method comprising the steps of: positioning thefirst detector head within a body cavity; positioning the seconddetector head external to the body part; using coincidence gating torecord data obtained by the first and second detector heads from theradiation emitted by the body part; and applying deterministic samplingusing Gaussian quadrature parameters to assist in an imagereconstruction or in an image formation using the recorded data.
 41. Themethod of claim 40, wherein the first detector head is coupled to aplurality of optical light fibers, and wherein the plurality of opticallight fibers are configured to be detachable from the first detectorhead.
 42. The method of claim 40, wherein the Gaussian quadratureparameters used for constructing the transition matrix are theGauss-Hermite weights w_(j) and abscissas q_(j).
 43. A method ofreconstructing image data to perform an endoscopic biopsy of a body partusing a positron emission tomography (PET) scanning system having atleast a first detector head and a second detector head, the first andsecond detector heads being sensitive to radiation emitted by the bodypart, and the method comprising the steps of: positioning the firstdetector head within a body cavity; positioning the second detector headexternal to the body part; using coincidence gating to record dataobtained by the first and second detector heads from the radiationemitted by the body part; and applying deterministic sampling usingGaussian quadrature parameters to assist in an image reconstruction orin an image formation using the recorded data.
 44. The method of claim43, wherein the first detector head is coupled to a plurality of opticallight fibers, and wherein the plurality of optical light fibers areconfigured to be detachable from the first detector head.
 45. The methodof claim 43, wherein the Gaussian quadrature parameters used forconstructing the transition matrix are the Gauss-Hermite weights w_(j)and abscissas q_(j).
 46. A method of reconstructing image data to detector delineate a lesion in a body part using a positron emissiontomography (PET) scanning system having at least a first detector headand a second detector head, the first and second detector heads beingsensitive to radiation emitted by the body part, and the methodcomprising the steps of: positioning the first detector head within abody cavity; positioning the second detector head external to the bodypart; using coincidence gating to record data obtained by the first andsecond detector heads from the radiation emitted by the body part; andapplying Monte Carlo methodology to assist in an image reconstruction orin an image formation using the recorded data.
 47. The method of claim46, wherein the first detector head is coupled to a plurality of opticallight fibers, and wherein the plurality of optical light fibers areconfigured to be detachable from the first detector head.
 48. A methodof reconstructing image data to select borders for amputation of a bodypart using a positron emission tomography (PET) scanning system havingat least a first detector head and a second detector head, the first andsecond detector heads being sensitive to radiation emitted by the bodypart, and the method comprising the steps of: positioning the firstdetector head within a body cavity; positioning the second detector headexternal to the body part; using coincidence gating to record dataobtained by the first and second detector heads from the radiationemitted by the body part; and applying Monte Carlo methodology to assistin an image reconstruction or in an image formation using the recordeddata.
 49. The method of claim 48, wherein the first detector head iscoupled to a plurality of optical light fibers, and wherein theplurality of optical light fibers are configured to be detachable fromthe first detector head.
 50. A method of reconstructing image data toperform an endoscopic biopsy of a body part using a positron emissiontomography (PET) scanning system having at least a first detector headand a second detector head, the first and second detector heads beingsensitive to radiation emitted by the body part, and the methodcomprising the steps of: positioning the first detector head within abody cavity; positioning the second detector head external to the bodypart; using coincidence gating to record data obtained by the first andsecond detector heads from the radiation emitted by the body part; andapplying Monte Carlo methodology to assist in an image reconstruction orin an image formation using the recorded data.
 51. The method of claim50, wherein the first detector head is coupled to a plurality of opticallight fibers, and wherein the plurality of optical light fibers areconfigured to be detachable from the first detector head.
 52. A methodof reconstructing image data to select borders for removal or killing ofpathological cells within a body part using a positron emissiontomography (PET) scanning system having at least a first detector headand a second detector head, the first and second detector heads beingsensitive to radiation emitted by the body part, and the methodcomprising the steps of: a) positioning the first detector head within abody cavity; b) positioning the second detector head external to thebody part; c) using coincidence gating to record data obtained by thefirst and second detector heads from the radiation emitted by the bodypart; d) applying Monte Carlo methodology to assist in an imagereconstruction or in an image formation using the recorded data; e)using the reconstructed or formed image to detect pathological cells; f)removing tissue from the body part based on the reconstructed or formedimage; and g) iterating steps a, b, c, d, e, and f to minimize an amountof residual viable pathological cells in the body part.
 53. The methodof claim 52, wherein the first detector head is coupled to a pluralityof optical light fibers, and wherein the plurality of optical lightfibers are configured to be detachable from the first detector head. 54.A method of reconstructing image data to select borders for removal orkilling of pathological cells within a body part using a positronemission tomography (PET) scanning system having at least a firstdetector head and a second detector head, the first and second detectorheads being sensitive to radiation emitted by the body part, and themethod comprising the steps of: a) positioning the first detector headwithin a body cavity; b) positioning the second detector head externalto the body part; c) using coincidence gating to record data obtained bythe first and second detector heads from the radiation emitted by thebody part; d) applying deterministic sampling using Gaussian quadratureparameters to assist in an image reconstruction or in an image formationusing the recorded data; e) using the reconstructed or formed image todetect pathological cells; f) removing tissue from the body part basedon the reconstructed or formed image; and g) iterating steps a, b, c, d,e, and f to minimize an amount of residual viable pathological cells inthe body part.
 55. The method of claim 54, wherein the first detectorhead is coupled to a plurality of optical light fibers, and wherein theplurality of optical light fibers are configured to be detachable fromthe first detector head.